The research proposed for this award will examine how spatial attention modulates cortical circuit activity in the early visual system. The proposed studies link the candidate's scientific background and future career objectives by examining attentional modulation of neuronal activity at multiple processing stages. Attentional effects will be observed at the individual cellular level (Aim 1), the local circuit level (Aim 2), and the cortical population level (Aims 1 and 3). By employing this novel approach toward understanding attention within the context of cellular and circuit processing, the candidate will draw upon experience across all phases of her research career. The candidate is nearing completion of the mentored phase where she has received outstanding mentorship from her two co-sponsors and has greatly benefited from the resources available at the University of California, Davis. According to the experimental plan laid out in Aim 1, the candidate has successfully measured attentional modulation of synaptic efficacy and cortical ensemble activity. The candidate has successfully implemented improvements in the attentional task and multi-neuron recording techniques which will greatly aid her transition and future success as an independent investigator. During the independent phase, the candidate will continue to address questions of functional dynamics in early visual cortical circuits using these improved spatial attention tasks and multi-electrode recording techniques. These experiments will further explore 1) whether and how the effects of spatial attention differ across neuronal cell types and local circuit levels, and 2) whether and how ongoing cortical network activity influences these attentional effects. All experiments proposed will be undertaken in the early visual system of awake-behaving monkeys, an ideal model for a number of reasons. First, while spatial attention influences early visual system activity, little is known about the mechanisms involved. Second, there is a wealth of knowledge available about the primate visual system. Third, the awake-behaving animal paradigm allows for the assessment of functionality in the fully cognizant state. Fourth, and most importantly, the primate visual system is similar to that of humans and therefore provides an ideal model for human cognition.